Yep you're right, I can't manage to download any previous version of Here WeGo manually. Not sure why. Maybe there is just no previous version available on the Play store, after all Yalp says that it is "sometimes" possible to download earlier versions, but it's not keeping copies of the files itself, everything is just downloaded from the Play store indirectly.

It may be worth asking on Yalp's github repository, the maintainer seems to be responsive and he also has some consideration for non Android-phones since he did include the Jolla C in the device-spoofing feature of his application.

In the meantime, maybe the best way is to find mirrors that keep version history.